Mechanistic Insights into Polypropylene Hydrogenolysis Using Ni/Al<sub>2</sub>O<sub>3</sub> Catalysts
Xiyan Huang, Weixin Meng, Diego A. Acevedo–Guzmán, Hongqi Wang, Balaji Sridharan, Petra Rudolf, Hero J. Heeres, Jingxiu Xie
Abstract
High Resolution Image Download MS PowerPoint Slide Catalytic hydrogenolysis is emerging as an attractive strategy for converting polyolefins into high-value hydrocarbon liquids. A key challenge in catalytic hydrogenolysis is the high methane yield. Recently, Ni-based catalysts have shown promise as a cost-effective alternative to noble metals in polyolefin hydrogenolysis. In this study, three alumina-supported Ni catalysts (12–13 wt % Ni) were prepared using acidic, neutral, and basic γ-Al 2 O 3 via impregnation. The resulting Ni/A-Al 2 O 3, Ni/N-Al 2 O 3, and Ni/B-Al 2 O 3 catalysts were used to investigate reaction pathways in n -hexadecane and isotactic polypropylene hydrogenolysis. Experiments conducted in a batch autoclave at 300 °C with 30 bar of H 2 showed that Ni/B-Al 2 O 3 exhibited the highest reactivity, 5 h for n -hexadecane and 30 h for polypropylene, respectively. Using n -hexadecane as a model compound for hydrogenolysis, we attributed the origin of methane selectivity to terminal C–C bond scission, occurring through both single-step and cascade mechanisms. Detailed product analysis (GC–FID, GPC, and NMR) and comprehensive catalyst characterization revealed the origins of varied activity and product distribution in the hydrogenolysis of n -hexadecane and polypropylene. The increased ratio of tetrahedrally coordinated Ni 2+ to metallic Ni 0, attributed to stronger metal–support interactions, along with stronger surface basicity, promotes terminal C–C scission, leading to enhanced hydrogenolysis reactivity.